Wash and scrub cucumbers carefully.,Cut 1/4-inch slice from blossom end of each cucumber.,Mix water, vinegar and salt in a Dutch oven; heat to boiling.,Place dill head and onion slice in each of 6 hot quart jars.,______,Cover with boiling brine, leaving 1/2-inch headspace. Wipe rims of jars.,Seal and process in boiling water bath for 10 minutes.